With the recent explosion of the use of wireless devices, the demand for better performing devices is greater than ever. Cell phones, tablets, or any other wireless devices can perform better by providing more computational power, higher downlink and uplink capacity, and more sensor capabilities, all without compromising battery life.
Battery life is directly related to the power consumption of the wireless device. One of the main power consumers in a wireless device is the power needed to transmit a signal. A power amplifier (PA) amplifies the outgoing signal to a desirable level and sends it to the antenna so that it can be converted to electromagnetic waves.
The problem with all antennas especially in a handheld device is that they do not maintain constant impedance. The antenna characteristics, including its impedance, change as the antenna moves within an environment, gets closer to different objects, etc. The change in the antenna impedance causes a mismatch between the antenna and the PA (or other blocks in the transmit path that interface with the antenna), which results in some of the outgoing signal to bounce back at the antenna. When this happens a portion of the signal is not transmitted. This is wasted energy. To compensate for it, the wireless device may increase the power, which further increases power usage. In a worst case, so much of the signal is bounced back and so little is transmitted to the air that it may lose contact with the base station. A combination of the reflected signal and the ongoing signal may also create an undesired standing wave. This standing wave may damage the circuit components such as the PA.
The antenna mismatch may also have other undesired effects such as the leakage of a portion of the transmit signal to the receive path. This is specifically problematic in communication systems that support simultaneous transmit and receive (STAR) capabilities, full duplex (FD) communications, and radar systems.
Antenna impedance can be extracted from the reflection coefficient. Many conventional approaches measure only the magnitude of the reflection coefficient, for instance, using a power meter and a directional coupler. As such, they do not provide information about the complex antenna impedance.
Some traditional schemes frequency-down-convert the reflected transmitting signals through a directional coupler. However, these schemes consume large chip area and power consumption due to the requirement for additional frequency downconverters (e.g., mixers), local oscillator buffers, and baseband circuitry.
In frequency division duplex (FDD) schemes, another challenge with conventional approaches is limited accuracy in the measurement of the reflection coefficient due to the simultaneous existence of receive and transmit signals.
In addition, existing approaches for measuring a complex reflection coefficient can be cumbersome, inefficient and costly. Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with the present disclosure as set forth in the remainder of the present application with reference to the drawings.